1. Field of the Invention
The instant invention relates to rotary compressors for automotive climate control systems. More particularly, the instant invention relates to a multi-stage rotary piston compressors having a plurality of valves to obtain continuous capacity control.
2. Description of the Related Art
When the air conditioning load in the passenger compartment of a vehicle is below a predetermined temperature, the displacement of a compressor within an air conditioning system of the vehicle can be decreased. This will result in a reduced compression ratio in the compressor and therefor a reduced cooling capacity.
It is known to vary the capacity of a compressor dependent upon operating requirements. An example of a compressor having capacity control is disclosed in U.S. Pat. No. 5,284,426, which is assigned to the assignee of the present invention. The '426 patent describes a refrigerant gas compressor having variable capacity control achieved by selectively disabling the outer vanes that cooperate with the outer perimeter of the orbiting ring piston. Either one or both of two outer vanes can be selectively disabled. However, the '426 patent decreases the compressor capacity in discrete steps.
It is also know to vary the capacity of a single stage compressor by valve means. An example of a single valve in a scroll type compressor is provided by Terauchio et al., U.S. Pat. No. 4,744,733. An example of such in a rotary type compressor is Goto et al., U.S. Pat. No. 4,566,863, which also teaches a single valve to open and close a by-pass passage.
However, neither Terauchio nor Goto provide the functional flexibility to match directly the compressor capacity with demand and neither teach how to do so with a compressor having multiple stages. The use of a single valve strictly limits the functional operating range of the capacity control. The limited functional range limits the decrease in parasitic loses and the overall horsepower savings of the air conditioning system. Further, the prior art compressors can only provide a restricted cycling map, in which it is necessary to cycle the compressor on/off with great frequency. The increased cycling frequency creates torque shock thereby increasing noise and vibration during compressor operation.
It is desirable to provide a multi-stage rotary piston compressor for automotive climate control systems which directly regulates compression volume in relation to demand. It is still further desirable to provide a multi-stage rotary piston compressor with a significantly increased cycling map.